Optical waveguides – With optical coupler – Input/output coupler
Reexamination Certificate
1999-09-21
2002-02-05
Mai, Huy (Department: 2873)
Optical waveguides
With optical coupler
Input/output coupler
C385S003000, C385S010000
Reexamination Certificate
active
06345136
ABSTRACT:
FIELD OF INVENTION
The present invention relates to a method, an arrangement and the use of an arrangement for tuneable add/drop multiplexing and for wavelength selective switching.
BACKGROUND OF THE INVENTION
There are known to the art a number of different methods for further enhancing the capacity of an optical transmission line (point-to-point connection) or in an optical network (multipoint-to-multipoint connection). One method involves the use of a so-called wavelength division multiplexing (WDM) technique for improving the extent to which available bandwidths are utilised on an optical fibre in the optical network, where the information is multiplexed with the aid of an optical wavelength multiplexer. The wavelength can also be used as an information address in an optical network. Enhancement of the flexibility of the network necessitates the presence of devices that are able to reroute traffic in the optical network. Such traffic rerouting devices, or arrangements, are also suitable for using the network in the most effective manner possible, and in the case of a network crash or gilch.
In the case of bus and ring networks for instance, add/drop multiplexers are central to effective communication with the network. It is important that the add/drop multiplexer can be tuned (change add/drop wavelength), when a node wishes to change communication channels. Swedish Patent Application SE 9700865-0 describes a wavelength selective 1-N switch and multi-add/drop with fixed add/drop wavelength channels.
This Swedish patent application also describes an arrangement which does not provide tuneable (selectable) add/drop multiplexing.
SUMMARY OF THE INVENTION
A number of different, known methods can be used to enhance the capacity of an optical transmission system.
In wavelength multiplexing, for instance, transmission channels are respectively multiplexed and demultiplexed to and from an information flow on different carrier wavelengths. This multiplexing and demultiplexing process requires the presence of optical wavelength selective devices. In bus and ring networks for instance, add/drop multiplexers are central to effective communication with the network. If a node wishes to change a communication channel, it is important to be able to tune the add/drop multiplexer (change add/drop wavelength).
One problem in this regard is that a known tuneable add/drop multiplexer may be consistent with high channel-dependent losses, crosstalk problems, and a high price.
The present invention addresses the aforesaid problem with a tuneable add/drop multiplexer that includes at least one MMI-waveguide, at least N-number of Michelson waveguides, where N≧4, at least one Bragg grating for each Michelson waveguide, and at least one phase control element in at least N−1 number of Michelson waveguides. The Michelson waveguides include said phase control elements and said Bragg gratings and are arranged for at least one MMI-waveguide. Each Michelson waveguide can be provided with a broadband reflection grating.
In a preferred embodiment, the broadband reflection gratings are arranged at the end of each Michelson waveguide.
In another embodiment of the inventive tuneable add/drop multiplexer, there is included at least one MMI-waveguide which is provided on a first side with at least four access waveguides and on a second side with at least four Michelson waveguides, one N-channel (de)multiplexer for each said Michelson waveguide, one reflection section per Michelson waveguide, wherein said reflection section includes N-number of Michelson waveguides for each said N-channel (de)multiplexer, wherein each such Michelson waveguide includes at least one Bragg grating, and wherein at least N-number of Michelson waveguides include at least one phase control element.
In another embodiment, the inventive tuneable add/drop multiplexer includes at least two MMI-waveguides, at least M-number of Michelson waveguides per MMI-waveguide, where M≧3, at least one Bragg grating per Michelson waveguide, and at least one phase control element in at least M−1 number of Michelson waveguides per MMI-waveguide. The Michelson waveguide includes said phase control element and said Bragg grating and is provided on a second side of the MMI-waveguides. An access waveguide provided on a first side of a first MMI-waveguide and an access waveguide provided on a first side of a second MMI-waveguide are mutually connected via a connection waveguide.
In a preferred embodiment of the aforesaid inventive, tuneable add/drop multiplexer, there is arranged an 1×N switch for each Michelson waveguide in connection with the second side of the MMI-waveguides, and a reflection section that includes said Bragg grating and said phase control element is provided for each such switch.
The MMI-waveguides are preferably a 3×3 type waveguide. The tuneable add/drop multiplexer may also include a broadband reflection grating for each Michelson waveguide. These gratings are preferably arranged at the end of each Michelson waveguide.
In a further embodiment of the inventive tuneable add/drop multiplexer, said M-number of Michelson waveguides, where M≧3, are arranged between a second side of the first MMI-waveguide and a second side of the second MMI-waveguide. Each Michelson waveguide includes at least two Bragg gratings, and at least M−1 numbers of Michelson waveguides include at least three phase control elements. The components thus function as an MMIMZI (Multi Mode Interference Mach-Zehnder Interferometer) for transmitted channels.
According to yet another embodiment of the inventive add/drop multiplexer, the multiplexer includes a third and a fourth MMI-waveguide. At least M-number of Michelson waveguides, where M≧3, are arranged between the third and the fourth MMI-waveguide. Each Michelson waveguide includes at least two Bragg gratings, and at least M−1 number of Michelson waveguides include at least three phase control elements. An access waveguide provided on the third or on the fourth MMI-waveguide via a connecting waveguide, and an access waveguide provided on the third MMI-waveguide is coupled to an access waveguide on the fourth MMI-waveguide via a connecting waveguide.
The third and the fourth MMI-waveguides are preferably of the 3×3 type.
The invention also relates to a first method for add/drop multiplexing optical waveguide channels in an optical network. Optical wavelength channels are excited into an access waveguide arranged on a first side of an MMI-waveguide. No optical add-wavelength channel or at least one optical add-wavelength channel is excited into a second access waveguide arranged on the first side of the MMI-waveguide. The optical wavelength channels, including the add-wavelength channel, are transmitted through said first MMI-waveguide and are imaged on at least one Michelson waveguide arranged on the opposite side relative to said access waveguide. The optical wavelength channels, including the add-wavelength channel, are transmitted through the Michelson waveguides. The phase of no optical wavelength channel or at least one of the optical wavelength channels is changed by any of the phase control elements in any of the Michelson waveguides.
At least one optical wavelength channel is reflected by a Bragg grating section arranged in the Michelson waveguide. No or at least one wavelength channel is dropped to a third access waveguide arranged on the first side of the MMI-waveguide. No or at least one wavelength channel is transmitted out through a fourth access waveguide arranged on the first side of the MMI-waveguide.
Those wavelength channels that have not been reflected by a Bragg grating can be reflected by a broadband reflection grating arranged in each of the Michelson waveguides.
The invention also relates to a second method for tuneable add/drop multiplexing of optical wavelength channels in an optical network. Optical wavelength channels are excited into a first access waveguide arranged on a first side of a first MMI-waveguide. The optical wavelength channels a
Burns Doane Swecker & Mathis L.L.P.
Mai Huy
Telefonaktiebolaget LM Ericsson (publ)
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